Transmission Device, Reception Device, Communication System, Control Circuit, Storage Medium, Transmission Method, and Reception Method

1. A transmission device to wirelessly communicate with a reception device, the transmission device comprising: modulation circuitry to perform frequency shift keying modulation on an input information bit sequence to generate a frequency shift keying symbol; direct-sequence spreading circuitry to spread the frequency shift keying symbol by direct-sequence spreading using a chirp sequence; and control circuitry to control a signal to be transmitted to the reception device in such a manner as to prevent a delayed-wave component in multipath propagation from appearing in a frequency shift keying candidate carrier in one symbol of two consecutive symbols, in a frequency spectrum of a signal obtained by despreading in the reception device.

2. The transmission device according to claim 1, wherein the control circuitry changes the carrier spacing of the frequency shift keying symbol on a per-symbol basis in such a manner that carrier spacings of the frequency shift keying symbols selected for the two respective consecutive symbols are prime to each other, and the modulation circuitry performs the frequency shift keying modulation on the basis of the carrier spacing of the frequency shift keying symbol determined by the control circuitry.

3. The transmission device according to claim 1, wherein the control circuitry changes the chirp sequence number on a per-symbol basis in such a manner that chirp sequence numbers selected for the two respective consecutive symbols are prime to each other and the direct-sequence spreading circuitry spreads the frequency shift keying symbol by direct-sequence spreading, on the basis of the chirp sequence number determined by the control circuitry.

4. A reception device to wirelessly communicate with a transmission device, the reception device comprising: despreading circuitry to despread a signal transmitted from the transmission device and received by the reception device; Fourier transform circuitry to perform Fourier transform on a signal obtained by despreading to generate a frequency signal; power calculation circuitry to calculate power of each subcarrier in the frequency signal; metric combining circuitry to add, on the basis of a number of delay samples of a delayed wave, power of a subcarrier at a position cyclically shifted in a forward direction by the number of delay samples from a candidate point of each frequency shift keying candidate carrier, to a metric of a corresponding frequency shift keying candidate symbol to calculate a combined metric; demodulation circuitry to perform a hard decision on the combined metric of each frequency shift keying candidate symbol, and to estimate a transmitted frequency shift keying signal from the transmission device; and delayed wave detection circuitry to detect a subcarrier having delayed-wave power residing therein, from the frequency signal, and to estimate the number of delay samples of the delayed wave from a difference between a position of the subcarrier carrying the delayed-wave power and a subcarrier position corresponding to the estimated transmitted frequency shift keying signal.

5. The reception device according to claim 4, wherein the delayed wave detection circuitry estimates the number of delay samples of the delayed wave by threshold-based determination using a statistical characteristic of noise.

6. The reception device according to claim 4, wherein the metric combining circuitry calculates the combined metric by a maximal ratio combining rule or a selection combining rule.

7. The reception device according to claim 4, wherein the delayed wave detection circuitry outputs the number of delay samples of the delayed wave estimated from a last one symbol or an average value of numbers of delay samples of a plurality of delayed waves estimated from a plurality of last symbols.

8. A communication system comprising: a transmission device; and the reception device according to claim 4, wherein the transmission device wirelessly communicates with the reception device, and the transmission device comprising: modulation circuitry to perform frequency shift keying modulation on an input information bit sequence to generate a frequency shift keying symbol; direct-sequence spreading circuitry to spread the frequency shift keying symbol by direct-sequence spreading using a chirp sequence; and control circuitry to control a signal to be transmitted to the reception device in such a manner as to prevent a delayed-wave component in multipath propagation from appearing in a frequency shift keying candidate carrier in one symbol of two consecutive symbols, in a frequency spectrum of a signal obtained by despreading in the reception device.

9. A control circuit for controlling a transmission device to wirelessly communicate with a reception device, the control circuit causing the transmission device to: perform frequency shift keying modulation on an input information bit sequence to generate a frequency shift keying symbol; spread the frequency shift keying symbol by direct-sequence spreading using a chirp sequence; and control a signal to be transmitted to the reception device in such a manner as to prevent a delayed-wave component in multipath propagation from appearing in a frequency shift keying candidate carrier in one symbol of two consecutive symbols, in a frequency spectrum of a signal obtained by despreading in the reception device.

10. A control circuit for controlling a reception device to wirelessly communicate with a transmission device, the control circuit causing the reception device to: despread a signal transmitted from the transmission device and received by the reception device; perform Fourier transform on a signal obtained by despreading to generate a frequency signal; calculate power of each subcarrier in the frequency signal; add, on the basis of a number of delay samples of a delayed wave, power of a subcarrier at a position cyclically shifted in the forward direction by the number of delay samples from a candidate point of each frequency shift keying candidate carrier, to a metric of a corresponding frequency shift keying candidate symbol to calculate a combined metric; perform a hard decision on the combined metric of each frequency shift keying candidate symbol, and estimating a transmitted frequency shift keying signal from the transmission device; and detect a subcarrier having delayed-wave power residing therein, from the frequency signal, and estimating the number of delay samples of the delayed wave from a difference between a position of the subcarrier carrying the delayed-wave power and a subcarrier position corresponding to the estimated transmitted frequency shift keying signal.

11. A non-transitory storage medium storing a program for controlling a transmission device to wirelessly communicate with a reception device, wherein the program causes the transmission device to: perform frequency shift keying modulation on an input information bit sequence to generate a frequency shift keying symbol, spread the frequency shift keying symbol by direct-sequence spreading using a chirp sequence, and control a signal to be transmitted to the reception device in such a manner as to prevent a delayed-wave component in multipath propagation from appearing in a frequency shift keying candidate carrier in one symbol of two consecutive symbols, in a frequency spectrum of a signal obtained by despreading in the reception device.

12. A non-transitory storage medium medium storing a program for controlling a reception device to wirelessly communicate with a transmission device, wherein the program causes the reception device to: despread a signal transmitted from the transmission device and received by the reception device, perform Fourier transform on a signal obtained by despreading to generate a frequency signal, calculate power of each subcarrier in the frequency signal, add, on the basis of a number of delay samples of a delayed wave, power of a subcarrier at a position cyclically shifted in the forward direction by the number of delay samples from a candidate point of each frequency shift keying candidate carrier, to a metric of a corresponding frequency shift keying candidate symbol to calculate a combined metric, perform a hard decision on the combined metric of each frequency shift keying candidate symbol, and estimating a transmitted frequency shift keying signal from the transmission device, and detect a subcarrier having delayed-wave power residing therein, from the frequency signal, and estimating the number of delay samples of the delayed wave from a difference between a position of the subcarrier carrying the delayed-wave power and a subcarrier position corresponding to the estimated transmitted frequency shift keying signal.

13. A transmission method for use in a transmission device to wirelessly communicate with a reception device, the transmission method comprising: performing frequency shift keying modulation on an input information bit sequence to generate a frequency shift keying symbol; spreading the frequency shift keying symbol by direct-sequence spreading using a chirp sequence; and controlling a signal to be transmitted to the reception device in such a manner as to prevent a delayed-wave component in multipath propagation from appearing in a frequency shift keying candidate carrier in one symbol of two consecutive symbols, in a frequency spectrum of a signal obtained by despreading in the reception device.

14. A reception method for use in a reception device to wirelessly communicate with a transmission device, the reception method comprising: despreading a signal transmitted from the transmission device and received by the reception device; performing Fourier transform on a signal obtained by despreading to generate a frequency signal; calculating power of each subcarrier in the frequency signal; adding, on the basis of a number of delay samples of a delayed wave, power of a subcarrier at a position cyclically shifted in the forward direction by the number of delay samples from a candidate point of each frequency shift keying candidate carrier, to a metric of a corresponding frequency shift keying candidate symbol to calculate a combined metric; performing a hard decision on the combined metric of each frequency shift keying candidate symbol, and estimates a transmitted frequency shift keying signal from the transmission device; and detecting a subcarrier having delayed-wave power residing therein, from the frequency signal, and estimating the number of delay samples of the delayed wave from a difference between a position of the subcarrier carrying the delayed-wave power and a subcarrier position corresponding to the estimated transmitted frequency shift keying signal.